Computer type brake analyzer

ABSTRACT

An apparatus for analyzing the performance of wheeled, land vehicle brake systems is described wherein means are provided for driving the vehicle wheels at a predetermined speed and the operator or computer controlled brake actuator selectively applies the brakes in a series of simple successive steps comprising the test sequence. The pedal force, or other actuating force, the brake effort exerted by each wheel, and the imbalance between the braking effort of opposite wheels is measured and recorded on a strip chart or fed to a computer, to determine if the measured values fall outside of a predetermined range of values representing acceptable deviations from standard values. Any deviation of the brake effort from the acceptable values, or excessive imbalance between opposite wheels at any point in the test sequence, may be used as a basis for diagnosing and identifying a specific brake malfunction. The system can be enlarged to simultaneously test the brakes on all wheels of a land vehicle.

BACKGROUND OF THE INVENTION Reference to Copending Application

This is a continuation in part application of copending application Ser.No. 382,538, filed July 25, 1973 now U.S. Pat. 3,899,916 which is acontinuation in part of application Ser. No. 811,168 filed Mar. 27,1969, now abandoned.

Field of the Invention

The present invention relates to improved apparatus and systems fortesting and diagnosing faults in wheeled, land vehicle brake systems.The invention particularly relates to a computer controlled or automaticbrake analyzer system to provide a rapid and reliable analysis ofvehicle brakes for purposes of safety and to facilitate repair ofdefective components.

The present invention is of great importance and practical value becausefaulty or inadequate vehicle brakes are one of the significantcontributing causes to the ever increasing number of automobileaccidents. It is well known that brake malfunctions caused by neglect,rather than poor brake design, are responsible for essentially allinstances of faulty or inadequate vehicle brakes. Furthermore, in amajority of instances, the neglect of vehicle brakes is not intentional.Rather, the owner simply is not aware of the existence of potentiallyhazardous conditions.

It is frightening to discover that faulty vehicle brakes frequentlyrespond normally under average driving conditions. Consequently, thedriver is lulled into a sense of false security concerning the adequacyof his brakes, and, therefore does not have them inspected, and iscompletely surprised when a malfunction occurs during emergencydeceleration or sudden stops. It is perhaps more unfortunate that asignificant number of potentially hazardous, but easily repairable,brake malfunctions are not discovered during routine inspection solelybecause prior existing inspection methods and equipment do not exposethem.

SUMMARY OF THE INVENTION

The present invention relates to a brake testing apparatus of highintegrity, which will detect nearly all types of brake malfunction,identify which brake is subject to the malfunction, and further indicatewhether the factor causing the malfunction is mechanical, hydraulic orfrictional. In many cases an even more specific cause of the detectedmalfunction can be readily determined and an accurate repair ticketimmediately prepared. Furthermore, the present invention relieves thetest operator of the task of reading output instruments or manuallyrecording indicated values during the test procedure and thereby reducestest time while greatly increasing accuracy and reliability.

The brake analyzing apparatus of the present invention includes meansfor selectively driving the wheels of the test vehicle. Thus, each wheelof the vehicle is cradled between a separate pair or rolls rotatablysupported by bearings mounted on a frame assembly. A cradle-mountedelectric motor is provided as a prime mover for each set of rolls andarranged to drive only the rear rolls of the set through a flexiblecoupling. Other forms of prime mover can be used, such as a hydraulic orpneumatic motor, or an internal combustion engine. All of these areparticularly suitable for portable brake testing apparatus. The rollsare driven at equal controlled speeds up to 45 MPH or more and in thepreferred form of apparatus, the brake effort is proportional to thereaction force upon each motor housing and is individually measured foreach wheel by a pneumatic weighing unit, or force transducer.

In performing a test, the operator or a computer controlled brakeactuator applies predetermined forces to the brake pedal, or other brakeactuating means, of the test vehicle in a predetermined testingsequence. When the vehicle brakes are actuated, the braking effortproduced at each wheel is proportional to the reaction force upon thecorresponding motor housing and is measured by the pneumatic weighingunit or other suitable transducer. Alternatively, the load current,torque or speed change of each driving motor can be measured as anindication of the braking effort being applied to its associated wheel.In the case of hydraulic or pneumatic motors, the pressure will increasewith load and provide an indication of torque output.

The measured values of brake effort are monitored during the test periodand an output signal, i.e., in the form of an indicating lamp, isproduced when the values of brake effort fall within or outside of apredetermined range of acceptable values. The strongest or weakest brakeis also identified to facilitate repair work. Standard values of brakeeffort for different weight classes of vehicles may be stored in asuitable memory and the set of values associated with a vehicle of agiven weight class may be chosen by the operator in order to allowinterchangeable testing of vehicles of different weights. The outputsignals may take the form of a lighted display, pumched cards or tape,or a printed sheet itemizing the necessary brake repairs.

An evaluation of the test results obtained is made against a set ofrealistic standard values previously determined through a carefulprogram of testing the behavior of vehicles equipped with brakes havingmalfunctions, repairing the malfunctions and again testing the behaviorof the vehicles with corrected brake systems. The standard valuesselected enable the behavior of the brakes of each vehicle tested to beclassified as satisfactory, marginal, or unsafe. Evaluation of the testresults is relatively simple and will identify nearly all conceivablebrake malfunctions. In most cases, an exact cause of the malfunction canbe identified by a specific symptom of the brake analyzer operation, andin all cases the cause or causes of the malfunction can be categorizedas either mechanical, hydraulic, or frictional, or a combination of twoor more of these factors.

In accordance with the present invention, an apparatus is provided foranalyzing the braking performance of a wheeled vehicle. The vehicle haswheel brakes associated with at least two of the wheels and a brakeactuator for simultaneously applying the brakes of said wheels. Theapparatus includes test means such as a dynamometer for rotating thewheels of the vehicle for a test period during which the brakes areapplied. Brake effort signal generating means are included as a part ofthe test means for producing a separate brake effort signal for eachwheel while the wheel brakes are being applied. Means are provided torespond to tbe brake effort signals and to the operation of the brakeactuator for producing a brake system response signal proportional tothe time delay between the operation of the brake actuator and (1) theengagement of the first brake to engage or (2) the attainment of apreset brake effort level. The apparatus may further include meansresponsive to the brake system response signal for producing asatisfactory or fail brake system response signal when the brake systemresponse signal is less than or exceeds a preset maximum acceptablevalue. In the alternative, the brake effort level reached by the wheelbrakes after a preset time delay from the operation of the brakeactuator may be measured and compared with a preset acceptable value.

BRIEF DESCRIPTION OF THE DRAWINGS

The construction and operation of the invention, as well as additionalobjects and advantages thereof, will become apparent when the followingdescription is read in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic view of a brake testing apparatus in accordancewith the present invention;

FIG. 2 is a plan view of the brake pedal control unit 332 of FIG. 1illustrating the placement of the operator's feet thereon in dottedlines;

FIG. 3 is a block diagram of a computer, control and sensor units foruse with the apparatus of FIG. 1;

FIG. 4 is a block diagram of analog to digital converters for convertingthe analog brake effort and pedal force signals to digital format;

FIG. 5 is a block diagram of certain vehicle test limit storage elementsfor use in the circuit of FIG. 3;

FIG. 6 is a block diagram of a programmer for use in the computer ofFIG. 3;

FIG. 7 is a block diagram of certain computer components for providingrolling resistance test data;

FIG. 8 is a block diagram of certain computer components for calculatingand storing the pre-hydraulic brake effort level;

FIG. 9 is a block diagram of certain computer components for providingsystem response test data;

FIG. 10 is a block diagram of another embodiment for providing systemsresponse test data; and

FIG. 11 is a block diagram of another embodiment for providing systemresponse data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A computer controlled or automatic brake analyzer system for testingvehicle brakes is described in FIGS. 1, 2 and 3. Referring now to FIG.1, a four-wheeled vehicle is illustrated with the front wheels 11 and 12cradled between the rollers 14 through 17 of a motoring dynamometer. Therolls 15 and 17 drive the wheels during the test, as will appear later.The rolls 14, 15, 16 and 17 are rotatably supported by bearings mountedin a conventional frame assembly, not shown. The rolls and frameassembly may be arranged in any convenient manner to permit the wheelsof the test vehicle to be easily stationed thereon. In an exemplaryinstallation the frame assembly may be mounted in a pit with the rollsat the floor level so that the test vehicle may be readily driven on andoff the rolls. The rolls 15 and 17 are oriented so that they arefarthest from the front end of the vehicle during a test.

Cradle-mounted electric motor 21 and 22 are provided as driving meansfor the left and right rolls 15 and 17, respectively. The shafts of themotors are directly coupled to the shafts of the respective drive rolls15 and 17 by suitable flexible couplings (not shown). The front rolls 14and 16 are permitted to idle.

A careful balance of motor power and roll spacing is necessary in thedescribed apparatus in order to permit accurate simulation of on-highwayspeeds and braking conditions. Thus, it has been found that the brakeheat produced in stopping a vehicle traveling 60 MPH is about nine timeshigher than that produced in stopping from 20 MPH. A high integritytesting system must have sufficient power to produce such heat at thebrake friction surfaces in the time consumed in a normal highway stop.Thus, neglecting vehicle wind resistance as a retarding force, a 0.5 Gdeceleration of a 4000 lb. vehicle from 60 MPH to 0 MPH results in anaverage brake heating rate of 113 btu/sec over a stopping time of 5.48sec. This power requirement can be met by application of 40 horsepowerat each wheel to be tested.

Although on-highway brake friction surface rubbing velocities decreaseas the vehicle decelerates, it has been found that test integrity isaffected only at extremely high speeds resulting in low brakeapplication forces for a given heating rate and at speeds below thecritical rubbing velocity of the friction surfaces. Thus, integrity maybe retained when tests are performed at one speed so long as the speedselected falls within the wide limits set forth above.

Selection of a particular speed is also dependent upon the tractiveeffort between the driving rolls 15 and 17 and the tire tread. When avehicle tire is cradled between two rolls as shown in FIG. 1, pressuresless than road contact pressures are present between the tires and eachroll. The pressure normal to the roll surface is dependent upon both theroll spacing and the particular roll from which the turning force isapplied to the tire. Thus, it should be apparent that as the brakes areapplied against rotating drive rolls 15 and 17, the vehicle will tend tomove backward. This will reduce the tire contact pressure against theforward idle rolls 14 and 16 and increase the tire contact pressureagainst the rear drive rolls 15 and 17. Accordingly, application ofpower to the tires through the rear drive rolls 15 and 17, as shown inthe preferred embodiment, has the advantage of increasing thetire-to-roll contact pressure as the brakes are increasingly applied.

The motors 21 and 22 are controlled from a motor by computer 299 throughlines 21c, d and e to provide a high torque, low torque and to stop. Apair of pneumatic lifts 300a and 300b are positioned between the rollsas illustrated to lift the wheels 11 and 12 off the rollers 14 through17 in their raised position and thereby permit the test vehicle to bereadily driven on and off of the rollers. Once the appropriate wheelsare positioned between the rollers 14 through 17, the pneumatic liftsare operated by means of appropriate electronic control units such as302a. The electronic control units operate fluid power lift units (303in FIG. 1) to lower or raise the lifts in response to appropriatecontrol signals on lines 304 and 305, respectively from the computer299. The lift control units 302a send back a lift lowered signal vialine 306 to the computer 299 indicative of the fact that the lifts arein a lowered position so that a selected testing sequence can begin.

Each motor 21, 22 is cradled as in a dynamometer so that a forcereaction can be measured from its housing, which is equal to the inputforce to the rolls and tires. Consequently, as the brakes are applied,their torque resistance to wheel rotation is proportional to motorhousing reaction. Since the right and left rolls are not interconnected,the retarding force from each brake can be independently measured by anysuitable electrical transducers which provide an output signalproportional to the torque between the respective housing of motors 21and 22 and the fixed rame. For example, brake effort signal generatingtransducers 38a and 39a are connected to the motors 22 and 21 to provideoutput signals representative of the torque applied by the drive motorswhich, in turn, is representative of the retarding force between therespective wheels and the drive rollers 15 and 17. Only one brake efforttransducer 39a is shown in FIG. 1 for purposes of illustration. For amore detailed discussion of transducers suitable for measuring the brakeeffort exerted on a motoring dynamometer, see British Pat. No. 1,284,498which issued on Dec. 6, 1972.

A pair of tachometer generators 307a and 307b are coupled to the drivenrollers 16 and 14 for providing d.c. signals to the computer via lines308a and 308b having an amplitude proportional to the speed of therespective driven roller. Only generator 307a is illustrated in FIG. 1.

The test vehicle illustrated in FIG. 1 is provided with conventionalbrake drums and shoes with the brake shoes 320 being forced outwardlyagainst the drums 321 by a manually controlled force responsive brakeactuator including a pair of conventional pistons 322 carried within awheel cylinder 323. Brake fluid is forced through brake lines 324 tooperate the wheel cylinder pistons 322 and apply the brakes by means ofa conventional master brake cylinder 325 including a piston 326 operatedby brake lever 327 in response to a force applied to a brake pedal 328.The brake lever 327 is biased by a spring 330 in a position to maintainthe brake pedal in its uppermost position to relieve the pressure in thebrake lines and permit the brake shoes 320 to be withdrawn from thebrake drum by conventional springs, not shown.

A brake pedal actuator control unit 332 for applying a programmed forceto the brake pedal 328 is described more particularly in the copendingapplication Ser. No. 382,538 filed July 25, 1973, and assigned to theassignee of this application. The unit 332 includes a frame 333 whichcomprises a pair of L-shaped legs which rest on the floor 334 of thevehicle under test. A foot treadle 335 is pivotally mounted at the lowerend of the frame 333. A piston 336 is mounted within a fluid powercylinder and forces a brake pedal bracket 337 against the brake pedal328 in accordance with the pressure of the fluid on the piston 336. Apedal force sensor (transducer) 333 is disposed between the bracket 337and the brake pedal 328 to provide an analog signal on line 340 which isproportional to the force applied to the brake pedal. A pedal-to-floordistance sensing unit 342 provides an output signal on line 343 when thepedal position has become less than the minimum acceptablepedal-to-floor distance.

The foot treadle 335 is biased outwardly away from the frame 333 bysuitable springs (not shown) with a force in excess of the maximum pedalforce required during the testing sequence. A foot pressure sensor inthe form of a micro-switch 345 is actuated when the force exerted by theoperator's feet on the treadle 335 exceeds the maximum anticipated pedalforce, causing the treadle to move downwardly a predetermined distanceagainst the spring bias. The foot pressure sensor 345 when actuatedproduces a foot pressure sensor signal on line 346 indicating that theoperator is placing sufficient force against the treadle 335 to preventmovement of the brake pedal actuator control unit while the brake pedalis operated at maximum force by the piston 336. Fluid under pressure isapplied to the piston 336 for operating the brake pedal via pneumaticline 350 and pedal actuator transducer 351. A pedal position transducer(not shown) is suitably secured to the fluid cylinder for generating asignal on line 348 which is proportional to the position of the piston336, for providing information concerning the brake pedal travel duringthe testing sequence as will be discussed in more detail.

The brake pedal control unit 332 is manually placed within the testvehicle at the beginning of the testing sequence. The operator guidesthe brake pedal bracket 337 until it engages the brake pedal 328 asshown in FIG. 1. An additional micro-switch may be positioned on thebracket 337 to be actuated when the bracket engages the brake pedalthereby providing a signal indicating that the control unit is in place.Rather than remove the brake actuator control unit 332 from the vehicleduring the time that the vehicle is moved to change the pair of wheelsthat are positioned on the dynamometer rollers 14 through 17, thecontrol unit 332 may be left in the vehicle and the brakes controlled bythe computer. To provide this type of control, a treadle sensor signalproportional to the force applied by the operator to the treadle may beproduced by a suitable transducer and fed back to the computer via line354. The compouter responds to the treadle sensor signal on line 354 toactuate the pedal actuator transducer 351 and apply fluid pressure tothe piston 336 which is proportional to the pressure of the operator'sfeet on the treadle. Such a transducer is described more particularly incopending application Ser. No. 382,538. The operator is thus providedwith reliable control of the braking action of the vehicle while it isbeing driven to place the rear wheels 11a and 12a on the dynamometerrollers.

Referring now to FIG. 3, the computer or automatic control system 299 isactuated by a manual control unit 353 to selectively commence the testsequence for the front or the rear wheels and to stop, via signals onlines 355, 356 and 357, respectively. The computer 299 receives inputsignals from the lift controls 302a and b indicating that the lifts arein the lowered position and the test vehicle wheels are properlypositioned for the test sequence. The computer also receives inputsignals from the brake effort transducers 38a and 39a, tachometergenerators 307a and 307b, foot pressure sensor 345, pedal-to-floordistance sensor 342, and pedal force sensor 338. The computer 299controls the induction motors 21 and 22 to provide high or low torque (yor Δ connection) or to stop, via signals on 21c, d and 3, respectively.The pedal actuator transducer 351 is controlled via signals on line 352to apply sufficient force to the vehicle's brake pedal to provide apredetermined brake effort from the strongest brake or a predeterminedpedal force as will be discussed in more detail.

The computer may provide output signals on line 361 for recording by aconventional recorder 362, for example, of the strip chart type ormagnetic type. The recorder 362 may also be in the form of a printerwhich provides a printed sheet indicating the condition of the vehiclebrakes, with or without recommendations as to suggest corrective workneeded, if any. The computer may also apply output signals on line 363to a visual display arrangement 364 such as a group of lights to providea recorded indication of appropriate output signals indicating thatcertain braking characteristics are satisfactory, marginal orunacceptable. The visual display arrangement provides a recordation ofsuch output signals for a time duration in excess of the testing periodso that the operator may review the braking performance after thetesting sequence has been performed on front, rear or both sets ofwheels of the test vehicle.

To determine whether or not the braking performance of the vehicle undertest is satisfactory, marginal or unacceptable, pre-established testlimits are fed into the computer on line 365 from a vehicle test limitsstorage arrangement 366, shown in more detail in FIG. 5.

The computer 299 operates on digital signals and thus includesconventional analog-to-digital converters for converting analog inputsignals into corresponding digital Analog-to-digital converters forproviding digital right and left brake effort signals and pedal forcesignals are illustrated in FIG. 4. Analog signals from the right andleft brake effort transducers 38a and 39a are amplified by amplifiers370a and 370b and converted to binary signals by analog-to-digitalconverters 371a and 371b. The binary signals representing the right andleft brake efforts are supplied on lines 372a and 372b to logic andstorage elements within the computer as will be described in moredetail. The lines such as 372a and 372b for carrying digital informationin the form of multi-bit words between the various computer componentsillustrated in the drawings are composite lines, that is, one line isused for each bit or N lines for an Nth bit word to transfer the data inparallel form. Thus, each digital data transmission line as shown in thedrawings represents a composite of Nth lines.

A subtractor 374 subtracts the digital signals representing the rightand left brake efforts to produce a braking effort imbalance signal online 375. Analog signals representing the separate brake effort signalsare also supplied to certain computing components via lines 373a and373b. The right and left brake effort signals on lines 372a, 372b, 373aand 373b represent the gross braking effort or the total retarding forcebetween the left or right wheel 11 or 12 and the respective drive roller15 or 17. During the time that the brakes are not being applied to thevehicle, the signals on lines 372a, 372b, 373a and 373b representrolling resistance of the respective wheels and when the brakes arebeing applied, these signals represent the sum of the rolling resistanceand the braking effort contributed by the brake drum and shoe of therespective wheel.

The brake effort imbalance signal on line 375 represents the grossimbalance in the retarding force between the wheels 11 and 12 and therespective drive rollers and thus includes the rolling resistanceimbalance of the two wheels. The subtractor 374 also applies an outputsignal on line 376 having a logic sign (high or low) dependent uponwhich brake effort signal is the largest. The logic sign of the signalon line 376 thus identifies the strongest (and weakest) brake. Forexample, a true logic signal (high level) on line 376 may be utilized toindicate that the highest brake effort is supplied by the right brakeand a false logic (low level) signal may be used to indicate that theleft brake is strongest.

A gate 379 receives the highest brake effort identification signal (trueor false) and switches the highest brake effort signal (right or left)to an output line 378. The analog signal from the pedal force sensor 338is also amplified by amplifier 380 and converted via ananalog-to-digital converter 381 to a binary signal representative of theforce applied to the brake pedal 328 (FIG. 1) by the pedal actuator 332(FIG. 1).

Referring now to FIG. 5, there are illustrated vehicle test limitsstorage elements 384a through 384jj for supplying digital signalsrepresenting satisfactory, marginal and unacceptable limits of brakeperformance of the vehicle under test and the brake effort levels atwhich the tests are to be conducted. The storage elements of FIG. 5provide a total of 36 output signals on lines 385a through 385jj to thecomputer. The circuit associated with each of the output lines 385athrough 385jj may be of the type shown in FIG. 6 of copendingapplication Ser. No. 382,538. The output signal for any line 385athrough 385jj may represent 210 or a total of 1024 discrete values.

The storage element 384a of FIG. 5 determines the total brake effortrequired (front plus rear wheel brakes) for the high level brake efforttests for the particular vehicle. The high level brake effort signal online 385a may be selected from as many as 1024 discrete values but as apractical matter may be limited to five values representing categoriesof weight of the vehicles being tested. Such categories may, forexample, represent (1) small cars, (2) intermediate compacts, compactcars, (3) heavy compact cars, (4) standard cars, and (5) heavy cars. Thestorage element 384b provides an output signal on line 385b whichrepresents the brake effectiveness percentage between the front and rearwheels of the vehicle under test. For example, the storage element 384bmay be set to provide a brake effectiveness of 75% for the front wheelsand 25% for the rear wheels, or 60% for the front wheels and 40% for therear wheels, etc. A 1 percent variation may be utilized if desired. Thestorage element 384c provides an output signal representing thepre-hydraulic brake effort factor X₁ which is utilized by the computerto arrive at the degree of braking effort utilized to derive certaintest data from the vehicle in pre-hydraulic tests as is described inmore detail in copending application Ser. No. 382,538. The storageelement 384d provides an output signal which represents a comfort levelbrake effort factor X₂ which is utilized by the computer to derive thecomfort level brake effort at which brake effort imbalance of thevehicle is measured as is described in copending application Ser. No.382,538. The storage element 364m and 384n provides output signals onlines 385m and 385n which represent the satisfactory and marginal limitsof brake system response time delays. The remaining storage elementsprovide signals representing satisfactory, marginal or acceptable limitsfor other brake tests for the particular vehicle under test and thevalue of such signals may be varied in accordance with brakingperformance requirements dictated by governmental agencies, etc.

It should be noted that only two output signals are utilized from eachof the storage elements 384stuv and 384wxyz at any one time, and the twoparticular output signal lines that are read by the computer will bedetermined by the type of brake incorporated into the test vehicles,that is, manual or power brakes.

The vehicle test limit information stored in elements 384a through 384jjmay, of course, be supplied to the computer by other well knownrecording means such as punched cards, magnetic tape, etc.

A computer programmer is illustrated in FIG. 6 for providing thecommands for a complete testing sequence for the front and rear wheelsof the test vehicle. The manual control 353 initiates the testingsequence for the front wheels by an appropriate signal on line 394 andinitiates the testing sequence of the rear wheels by a signal on line395. The manual control unit stops the test program and the dynamometermotors by a signal on line 396. A signal on line 394 or 395 actuates apre-program storage register 400 to provide a signal on line 304 tocause the lift control units to lower the lifts and cradle the frontwheels between the rollers 14 through 17. The storage register 400 alsoprovides a signal on line 352 to the pedal actuator transducer 351 tocause the brake pedal actuator 332 to lower the brake pedal bracket 337until contact is just made with the brake pedal 328. The brakes are notapplied by the signal on line 352 from the register 400.

As shown in FIG. 6, signals on lines 394 and 395 from the manual control353 are also applied to front and rear wheel test inhibitors 402a and402b. The wheel test inhibitors also receive signals from the footpressure sensor 345 via line 346 and from the lift control units vialine 306. An appropriate signal (true or false) on all input circuits ofeither wheel test inhibitor will provide an output signal (i.e. true) onthe respective output lines 403 and 404 or 407, 408 and 409.

Front and rear wheel lamp indicators 410 and 412 are responsive tosignals on lines 403 and 407 to indicate which set of wheel brakes areundergoing tests. An output signal on line 404 or 409 initiatesoperation of the motor control 413 which, in turn, applies anappropriate signal on output line 21d to energize the inductiondynamometer motors 21 and 22 in a low torque configuration, e.g. Yconnection. The dynamometer motors rotate drive rollers 15 and 17 which,in turn, rotate the left and right wheels of the vehicle. The vehiclewheels, in turn, drive the driven rollers 16 and 14 which rotatetachometer generators 307a and 307b. Under certain abnormal conditionssome slippage may occur between the tires and the drive rollers 15 and17 which causes the driven rollers 14, 16 to rotate at a slower speedthan the drive rollers 15, 17. The coefficient of friction, influenced,for example, by water between the tires and rollers is an importantfactor in determining slippage. Thus, the driven rollers 14 and 16 willbegin to catch up to the drive rollers 15 and 17 as the surface of thetires dry off.

Each of the tachometer generators 307a and 307b produce a d.c. signalhaving a magnitude proportional to the rotational speed of therespective driven rollers 16, 14. The signals from the tachometergenerators are supplied to one input of a pair of differentialamplifiers 416 and 418. The other input of each of the differentialamplifiers is connected to a reference voltage source 417. Thedifferential amplifiers 416 and 418 are arranged to provide anappropriate output signal (high level) to a gating circuit 414 only whenthe output signal from the respective tachometer generator exceeds thereference voltage. An output signal from each differential amplifier isindicative of the fact that both driven rollers are within apredetermined range of the normal induction motor speed representing,for example, a vehicle speed of 45 MPH.

A gating circuit 414 produces an output signal on line 420 in responseto output signals from both comparators 416 and 418 and an output signalon line 404 or 409. The output signal on line 420 causes the motorcontrol unit 413 to change the energization to the drive motors to ahigh torque configuration e.g., Δ connection, via a signal on line 21c.An output signal on line 420 is also supplied to a program commandstorage 422 to initiate time sequence test commands to the variouscomponents of the computer as will be described in more detail. Forexample, the program command storage provides command signals to a frontto rear pedal force balance command control unit 425. The unit 425 inresponse to the command signal from storage 422 and a signal from therear wheel test inhibitor via line 408 provides a signal to the pedalactuator transducer 351 to actuate the brakes in the front to rear pedalpressure balance tests to be described.

The program command storage also provides appropriate signals to commandunit 427 to initiate a static pedal force and pedal to floor test. Atthe end of a test sequence, the program command storage supplies asignal to an end of test control unit 430 which sends a signal on line305 to the lift control units to raise the lifts so that the vehicle maybe moved. A manual pedal control unit 432 when enabled by a signal fromunit 430 responds to a signal from the treadle pressure sensor on line354, and provides a signal proportional thereto on line 352 to controlthe brake pedal actuator 332 in accordance with the operator's footpressure on the treadle. This permits the vehicle to be moved withoutremoving the actuator 332. The manual pedal control unit 432 isinhibited by a signal on either line 404 or 409 indicating that a testsequence is still under way. Fast and slow rate pedal force controlunits 434 and 435 apply signals to the pedal actuator transducer 351 toprovide a fast or slow rate of brake application as will be described.

The detailed function of the components of the automatic control system299 for controlling the vehicle brakes and for monitoring the brakingeffort signals etc., in a multi-step testing sequence is described indetail in my copending application Ser. No. 381,538. Only thosecomponents and testing steps which relate to the present invention ofapparatus for evaluating brake system response test data is described indetail here.

Preparatory to commencing the test sequence, it is necessary that eachof the vehicle test limit storage elements 384a through 384jj beadjusted to provide the appropriate output signal. The category ofweight of the vehicle, i.e., compact, etc., percent of balance betweenfront and rear brakes, use of power or manual brakes are reflected byappropriate adjustments in storage elements 384a and 384b, 384stuv and384wxyz. The acceptable or marginal and fail limits as established bythe remaining storage elements will remain the same for many vehicles.

An anti-skid and limited slip differential switch may also be manuallyset by the operator prior to the commencement of the test sequence. Ananti-skid switch (not shown) permits the operator to determine whetherthe anti-skid test will be performed on the front and/or rear wheelbrakes. A limited slip differential switch permits the operator tooverride an abort command when the maximum rolling resistance of eitherwheel exceeds a preset maximum limit as is described in more detail inconnection with FIG. 7.

To initiate the test sequence, the vehicle is driven into the test areauntil the front wheels are positioned between the dynamometer rollers 14through 17 (FIG. 1). The brake pedal actuator control unit 332 ispositioned over the brake pedal and the pedal bracket 337 is positionedover the brake pedal and the pedal bracket 337 is guided into engagementwith the brake pedal. The manual control 353 is then actuated by theoperator while seated behind the vehicle steering wheel to initiatetesting of the front wheels.

Referring now to FIG. 6, the hydraulic lifts are lowered by thepreprogrammed storage register 400 and the motors are energized in thelow torque configuration as discussed previously. When the drivenrollers 14 and 16 have reached a predetermined percentage of the test orinduction motor speed, i.e. 75%, the gating circuit 414 actuates themotor control 413 to energize the dynamometer motors in the high torqueconfiguration. The gating circuit 414 also provides a signal to theprogram command storage which, after a predetermined time delay, forexample, 2 seconds to enable the dynamometer rollers to arrive at thefinal test sequence speed, e.g. 45 MPH, issues test commands to thevarious components to the system to begin the testing operation.

ROLLING RESISTANCE STORAGE AND EVALUATION TEST

The maximum rolling resistance and the rolling resistance imbalance aremeasured and compared with maximum, satisfactory and marginal presetlimits by the computer components illustrated in FIG. 7. The rollingresistance of each wheel is also stored during this testing step for usein later testing steps in providing the net brake effort imbalance. Theprogrammer illustrated in FIG. 7 is shown only in block form andreferenced by the number 440. The programmer initiates operation of thevarious components of FIG. 7, i.e., gates and storage elements andcontrols the brake pedal actuator via signals to the transducer 351 tomaintain the brakes in a released or inoperative condition. The signalson lines 372a and 372b thus represent the rolling resistance of theright and left wheels of the vehicle. The rolling resistance signals areapplied to a dual subtractor 442 and stored in storage elements 455 and456. The subtractor 442 subtracts the right and left rolling resistancesignals from a maximum limit rolling resistance signal from storageelement 384e. The subtractor 442 applies a first output signal (e.g.high level) on fail lines marked F, to associated gates 446 or 447 wheneither rolling resistance signal exceeds the maximum limit signal fromelement 384e. The gates 446 and 447 are enabled by an appropriatereadout command signal from the programmer 440 and in response to a failsignal from the dual subtractor 442 to energize a fail lamp indicator452 or 453, respectively, indicating that the rolling resistance of therespective wheel has exceeded the acceptable limit. The satisfactoryindicating lamps 450 and 451 are energized when the subtractors apply asecond output signal on S or satisfactory lines to the gates 446 and 447indicating that the rolling resistance is less than the maximumacceptable limit. The indicating lamps 450 through 453 remain energizedby an appropriate latching circuit to be discussed, until after the testsequence has been completed to provide a recorded indication that thevehicle has passed or failed the maximum rolling resistance test. Theindicating lamps referred to in the remaining figures also remainenergized for a period in excess of the test period to provide a recordof the test results.

The automatic control system of the present invention includes a limitedslip differential switch 448 and a limited slip differential abortcommand gate 449 as shown in FIG. 7. A fail signal on line F from thedual subtractor 442 is also applied to the programmer 440 via abortcommand gate 449 to stop the testing sequence and de-energize thedynamometer motors 21 and 22. The limited slip differential switch 448when operated to indicate that the vehicle being tested is equipped withlimited slip differential inhibits the abort command gate 449 during therear wheel testing sequence so that a fail signal on line F from thesubtractor 442 does not stop the testing sequence.

During the rolling resistance test, the highest rolling resistancesignal on line 378 is stored in storage element 457 for later use. Thebrake imbalance signal on line 375 is also stored in storage element 458and compared with the satisfactory and marginal preset imbalance limitsvia a dual subtractor 459. When the brake effort imbalance signal on 375is greater than the marginal preset limit from storage element 384g,then the subtractor 459 applies an appropriate output signal (e.g. highlevel) on output line F to gating circuit 462 to cause either a left orright fail indicating lamp 463 or 466 to be energized. When theimbalance signal on line 375 is less than the marginal preset limit butgreater than the satisfactory preset limit (384f) then the subtractor459 applies an appropriate output signal (output line M) to the gatingcircuit 462 which, in turn, energizes a marginal indicating lamp 464 or467. The gating circuit 462 is enabled by a readout command signal fromthe programmer 440 and is also responsive to the highest brake effortidentification signal on line 376 to transfer the output signals on thesubtractor output lines M or F to left or right indicating lamps. Wherethe left brake effort signal is the largest, the left indicating lamps(463, 464) will be energized and vice versa. When the imbalance signalon line 375 is less than the preset satisfactory level, then thesubtractor 459 applies an output signal on output line S to twosatisfactory indicating lamps 465 and 468 via the gating circuit 462.

The indicating lamps 450 through 453 and 463 through 468 inform theoperator that (1) the vehicle has passed or failed the maximum rollingresistance test, (2) the vehicle has a satisfactory, marginal orunacceptable rolling resistance imbalance, and (3) the identity of thewheel with the highest rolling resistance where the imbalance ismarginal or failing. The output signals from the gates 446 through 447and 462 may be utilized to operate a printer or other suitable recordingdevice, if desired.

SYSTEM RESPONSE TEST

In preparation for the brake system response test, the computercalculates the pre-hydraulic brake effort level for use in controllingthe brake pedal actuator. The components for performing this calculationare illustrated in FIG. 8. The value of the high level brake effort forthe front or rear wheel testing sequence is obtained by a divider 469which divides the total brake effort value stored in element 384a by anumber representing the percentage of such value to be used in testingthe front or rear wheel brakes, i.e. 75%, 25%, etc.. The highest rollingresistance value Z as stored in element 457 in the previous test issubtracted via subtractor 470 from the output signal Y of the divider469. The prehydraulic brake effort factor X₁ which has been preset intoelement 384c is divided into the difference signal Y-Z from thesubtractor 470 by a divider 471. The quotient ##EQU1## is then added tothe stored highest rolling resistance signal Z by an adder 472 and theresultant signal is stored in storage element 473.

The system is now ready for the brake system response test. Referringnow to FIG. 9, force is applied to the brake pedal at a high rate (e.g.90 lbs. of brake effort per second) via the high rate controller 434,the brake actuator transducer 351 and the brake pedal actuator controlunit 332. The brake pedal actuator continues to apply force to the brakepedal until the highest brake effort signal as measured reaches thepre-hydraulic brake effort level stored in element 473. It should benoted that the brake system response test could be performed byutilizing some value of brake effort in the element 473 other than thepre-hydraulic brake effort level calculated by the circuit of FIG. 8.

Upon the application of force to the brake pedal, the brake pedal forcesensor signal of line 340 (FIG. 4) starts an oscillator 524. The outputof the oscillator 524 is applied to a counter 525. At this same time, apair of increase in level detectors 526 and 527 provide a brakeengagement signal on line 528 to stop the oscillator 524 when either theright or left brake effort signal has increased a pre-determined amount(i.e. 3 lbs.) indicating that the brake has engaged. The increase inlevel detectors 526 and 527 may be the same type as the detector 475shown in FIG. 20 of copending application Ser. No. 382,538.

The count from the counter 525 is compared by the subtractors 530 and531 to preset satisfactory and marginal limits stored in elements 384mand 384n. The gating circuit 532 is enabled by the brake engagementsignal via gate 529 as illustrated. The gating circuit 532 when enabledresponds to the output signals from the subtractors 530 and 531 to (1)energize a fail indicating lamp 534 when the count is greater than themarginal preset limit (2) energize a marginal indicating lamp 535 whenthe count in counter 525 is between the satisfactory and marginal presetlimits, and (3) energize a satisfactory indicating lamp 536 when thecount is less than the satisfactory preset limit. The lamps 534, 535 and536 thus inform the operator of whether the brake system response timeis satisfactory, marginal or unacceptable. The lamps 534, 535 and 536remain energized for a time in excess of the time that the brakes arebeing applied during the test period to permit the operator to read thelamps after the test has been completed.

An alternative apparatus for performing a brake system responseevaluation test is illustrated in FIG. 10. This apparatus also appliesforce to the brake pedal via an actuator in the same manner as theapparatus of FIG. 9. Upon application of force to the brake pedal, thepedal force signal on line 340 starts the oscillator 524. The output ofoscillator 524 is also applied to the counter 525 and compared with thesatisfactory and marginal preset limits in the same manner as previouslydiscussed. In the apparatus of FIG. 10 the response time is measuredfrom the time that force is applied to the brake pedal until the highestbrake effort reaches a preset limit. To accomplish this objective, thehighest brake effort signal on line 378 is compared with a preset brakeeffort limit as stored in storage element 900 by means of a magnitudecomparator 902. When the highest brake effort signal reaches the presetlimit (for example, 150 lbs.) as stored in element 900, an output signalfrom the magnitude comparator 902 stops the oscillator 524 and enablesthe gating circuit 532 by means of the gate 529. The resulting count incounter 525 is thus equal to the time delay between the application offorce to the brake pedal and the attainment of a preset brake effort. Itshould be noted that the highest brake effort signal on line 378 may bemade equal to the highest net brake effort by subtracting the highestgross brake effort from the highest rolling resistance value stored inelement 457 of FIG. 7. The count in counter 525 is compared with presetsatisfactory and marginal limit values by means of subtractors 530 and531 as previously discussed.

As an alternative, the response of the brake system of a vehicle may beevaluated by measuring the highest brake effort achieved at the end of apredetermined time interval from the time that the brakes are applied.An apparatus for providing this type of data is illustrated in FIG. 11.In accordance with the apparatus of FIG. 11, the pedal force signal online 340 is applied to a system response delay circuit 904. The delaycircuit 904 is enabled by the programmer 440 and produces a readoutcommand signal to the gating circuit 532, a predetermined time intervalafter receiving the pedal force signal on line 340. During this presettime interval, corresponding to the delay of circuit 904, the highestbrake effort signal on line 378 is measured and compared with the valuesin satisfactory preset limit storage element 906 and marginal presetlimit storage element 908 by a dual subtractor 910. The dual subtractor910 provides output signals on output lines S, M and F indicating thatthe highest brake effort signal has exceeded the satisfactory presetlimit, remains between the satisfactory and marginal preset limits andfalls below the marginal preset limits, respectively. The gating circuit532 upon receipt of the readout command signal from the delay circuit904 samples the output lines from the dual subtractor 910 and energizes(1) satisfactory indicating lamp 912, (2) marginal indicating lamp 914or (3) fail indicating lamp 916 when the output lines S, M or F carrythe output signal of the dual subtractor 910, respectively.

The brake analyzer apparatus and method of my invention described abovemeasured and compares certain braking performance characteristics suchas brake effort imbalance when the strongest brake reaches apredetermined brake effort, e.g., pre-hydraulic, comfort level and highlevel. It should be understood that the brake effort level used for suchtests may be the sum of the individual brake efforts of the two wheelbrakes under test instead of the brake effort reached by the strongestbrake. It is only necessary that at least one of the brake effortsignals (e.g., one or the sum of both signals) reach a signalrepresentative of a pre-established brake effort to analyze certain ofthe vehicle braking performance characteristics discussed above.

Logic circuits which may be used in the block diagrams discussed inFIGS. 7, 9, 10 and 11 are illustrated in copending application Ser. No.382,538.

There has thus been described an automatic brake analyzer for evaluatingthe brake system response phenomena of a vehicle's brakes. Variousmodifications to the circuits will be obvious to those skilled in theart without departing from the scope of my invention as defined by theappended claims.

What is claimed is:
 1. In an apparatus for analyzing the brakingperformance of a wheeled vehicle having wheel brakes individuallyassociated with at least two wheels and a brake actuator forsimultaneously applying the brakes to said wheels, the combination whichcomprises:test means for rotating said wheels of the vehicle; brakeeffort signal generating means including the test means for producing aseparate brake effort signal for each wheel, the brake effort signalsbeing proportional to the brake effort of the respective wheel while thewheel brakes are being applied; and system response signal generatingmeans responsive to the brake effort signals and to the operation of thebrake actuator for producing a brake system response signal proportionalto the delay between the time that the brake actuator is operated and atleast one of the wheel brakes reaches a preselected brake effort.
 2. Thecombination as defined in claim 1 wherein said one wheel brake is thefirst brake to engage after operation of the brake actuator and thepreselected brake effort is equal to a nominal increase in the brakeeffort after operation of the brake actuator.
 3. The combination asdefined in claim 2 wherein the system response signal generating meansincludes a separate increase in level detector for receiving each of themeasured brake effort signals, each increase in level detector beingarranged to produce an output signal when the respective brake effortsignal increases in value a preset nominal amount.
 4. The combination asdefined in claim 3 wherein the system response signal generating meansincludes a brake actuator sensor for providing an output signal inresponse to operation of the brake actuator to apply the brakes.
 5. Thecombination as defined in claim 4 wherein the system response signalgenerating means includes a counter for providing the brake systemresponse signal proportional to the time interval between the outputsignal from the brake actuator sensor and the first output signal fromone of said increase in level detectors.
 6. The combination as definedin claim 5 including means responsive to the brake system responsesignal for producing a satisfactory or fail brake system response signalwhen brake system response signal is less than or exceeds a signalrepresenting a preset maximum acceptable value.
 7. The combination asdefined in claim 6 including means responsive to the brake systemresponse signal for producing a marginal system response signal when thebrake system response signal falls within a preset marginal range ofvalues.
 8. The combination as defined in claim 1 wherein said one wheelbrake is the brake which produces the highest brake effort and thepreselected brake effort is equal to a substantial increase in the brakeeffort after the operation of the brake actuator.
 9. The combination asdefined in claim 3 wherein the system response signal generating meansincludes a brake actuator sensor for providing an output signal inresponse to operation of the brake actuator to apply the brakes.
 10. Thecombination as defined in claim 9 wherein the system response signalgenerating means includes a magnitude comparator for producing an outputsignal when the highest brake effort reaches the preselected brakeeffort.
 11. The combination as defined in claim 10 wherein the systemresponse signal generating means includes a counter for providing thebrake system response signal proportional to the time interval betweenthe output signal from the brake actuator sensor and the output signalfrom the comparator.
 12. The combination as defined in claim 11including means responsive to the brake system response signal forproducing a satisfactory or fail brake system response signal when brakesystem response signal is less than or exceeds a signal representing apreset maximum acceptable value.
 13. The combination as defined in claim12 including means responsive to the brake system response signal forproducing a marginal system response signal when the brake systemresponse signal falls within a preset marginal range of values.
 14. Inan apparatus for analyzing the braking performance of a wheeled vehiclehaving wheel brakes individually associated with at least two wheels anda brake actuator for simultaneously applying the brakes to said wheels,the combination which comprisestest means for rotating said wheels ofthe vehicle; brake effort signal generating means including the testmeans for producing a separate brake effort signal for each wheel, thebrake effort signal being proportional to the brake effort of therespective wheel while the wheel brakes are being applied; and meansresponsive to the brake effort signals and to the operation of the brakeactuator for producing a brake system response signal proportional tothe time delay between the operation of the brake actuator and theengagement of the first brake to engage.
 15. The combination as definedin claim 14 including means responsive to the system response signal forproducing a satisfactory or fail brake system response signal when thesystem response signal is less than or exceeds a signal representing apreset maximum acceptable value.
 16. The combination as defined in claim15 including means responsive to the brake system response signal forproducing a marginal system response signal when the system responsesignal falls within a preset range of values.
 17. In an apparatus foranalyzing the braking performance of a wheeled vehicle having wheelbrakes individually associated with at least two wheels and a brakeactuator for simultaneously applying the brakes to said wheels, thecombination which comprises:test means for rotating said wheels of thevehicle; brake effort signal generating means including the test meansfor producing a separate brake effort signal for each wheel, the brakeeffort signal being proportional to the brake effort of the respectivewheel while the wheel brakes are being applied; and means responsive tothe brake effort signals and to the operation of the brake actuator forproducing a brake system response signal proportional to the delaybetween the time that the brake actuator is operated and the highestbrake effort signal reaches a preset system response limit.
 18. Thecombination as defined in claim 17 including means responsive to thesystem response signal for producing a satisfactory or fail brake systemresponse signal when the system response signal is less than or exceedsa signal representing a preset maximum acceptable value.
 19. Thecombination as defined in claim 18 including means responsive to thebrake system response signal for producing a marginal system responsesignal when the system response signal falls within a preset range ofvalues.
 20. In an apparatus for analyzing the braking performance of awheeled vehicle having wheel brakes individually associated with atleast two wheels and a brake actuator for simultaneously applying thebrakes to said wheels, the combination which comprises:test means forrotating said wheels of the vehicle; brake effort signal generatingmeans including the test means for producing a separate brake effortsignal for each wheel, the brake effort signal being proportional to thebrake effort of the respective wheel while the wheel brakes are beingapplied; and means responsive to the brake effort signals and to theoperation of the brake actuator for producing a satisfactory or failbrake system response signal when at least one of the brake effortsignals exceeds or remains below a preset minimum value at the end of apredetermined time interval after the operation of the brake actuator.21. The combination as defined in claim 20 including means for producinga marginal brake system response signal when at least one of the brakeeffort signals falls within a preset marginal range of values at the endof a predetermined time interval after the operation of the brakeactuator.
 22. The combination as defined in claim 20 wherein said onebrake effort signal is the highest brake effort signal.
 23. Thecombination as defined in claim 22 wherein the last named means includesa brake actuator sensor for providing an output signal when the brakeactuator is operated, a system response delay circuit responsive to theoutput signal from the brake actuator sensor for providing an outputsignal at a predetermined time interval after the brake actuator outputsignal and comparator means for comparing the highest brake effortsignal with a satisfactory preset limit and output signal generatingmeans coupled to the comparing means for producing unsatisfactory outputsignal in response to the delay circuit output signal when the highestbrake effort signal remains below the satisfactory preset limit.